Scharbert, Andreas Peter (2009) Community patterns and recruitment of fish in a large temperate river floodplain - The significance of seasonally varying hydrological conditions and habitat availability. PhD thesis, Universität zu Köln.
The seasonal occurrence of river temperatures in correlation to flood events is a key factor for lateral migrations, the recruitment dynamics and the related organisation of communities within different ecotones of the floodplain. The interaction of species-specific temperature requirements for spawning and reproductive strategies suggest adaptations to the long-term hydrograph, since the presence of species life-time stages within waterbodies are differently affected by seasonal inundations and recruitment patterns that occur along a hydrological gradient, thus, favouring different life-history strategies. Floodplain recruitment of most large species that mature late, with high fecundity and spawn comparably early in the season, is highly attributed to inundations occurring in this time-frame and resulted in massive larval peaks in all waterbodies affected by the connection to the main river. For some of these species which predominantly exhibit typical trait features associated with the periodic life-history strategy this adaptation to long-term discharge patterns is evident by lateral spawning migrations of adults. In contrast, the progeny of riverine spawning species enters the floodplain passively during flood events. Recruitment in some of these species in non-permanently connected floodplain waterbodies was drastically reduced, when no inundations occurred in the time-frame when their spawning takes place. The young-of-the-year (YOY) of these periodic strategists are mostly characterised by fast growth, which is favoured by the early spawning and is often accompanied by a diet specialisation. The relative large size of the YOY apparently influences habitat utilisation on different scales, since larvae and juveniles exhibit low preferences for sheltered microhabitats and emigrate from the floodplain at given connectivity in the course of the summer or at latest in winter. However, the timing of this shift differed between species belonging to different ecological guilds which YOY and older juvenile stages were entirely absent from the floodplain in the subsequent spring. Inverse adaptations to the long term hydrograph occur in predominantly small-sized species, which mature at young age, are less fecund and spawn at higher temperatures and over elongated periods of the summer. The YOY of these species attain only small until the end of summer. These features are closely associated to the opportunistic life-history strategy and imply competitive disadvantages towards faster growing species, which is expressed by a strong preference of YOY for densely vegetated microhabitats, increased mortalities and low recruitment when such habitats are lacking. Categorically small sized YOY exhibited more pronounced habitat requirements. Accordingly most of these species (e.g. Threespined stickleback, Japenese minnow, Sunbleak) had highest recruitment in waterbodies unaffected by inundations in spring and summer. This relationship is attributable to the lateral zonation of communities in the floodplain and suggests that remote and less frequently inundated waterbodies within the floodplain, which experience low disturbances and provide relatively constant habitat conditions (low water-level changes, abundant vegetation), are predominantly inhabited by opportunistic strategists. The temperature-dependent sequence of spawning in relation to inundation patterns and the habitat availability strongly influences the composition of the fish communities, however, also predator-prey interactions within the floodplain. At the example of two functionally different piscivores, which spawn in independency of inundations, it could be demonstrated that the onset of early piscivory is favoured by the earlier hatching and the faster initial growth compared to later spawning species. The maintenance of early piscivory depends on the size advantage over and the availability of smaller YOY fish prey. Due to prolonged spawning periods of multiple spawning species and high abundance of their small progeny (e.g. White bream), early piscivory of Pikeperch and Perch was favoured in lakes that were subject to repeated inundations, particularly when the required habitats of the potential prey species were lacking or became scarce during early summer. Therefore early piscivory was even enhanced in the less specialised Perch, particularly in waterbodies of low structural complexity like gravel pits, and YOY piscivores caused high mortalities in the small sized prey species. In contrast the occurrence and maintenance of early piscivory was impaired, when the size-advantage towards other members of the YOY community decreases, as well as in lakes with high structural complexity. In conclusion, the findings of this thesis suggest that the affectation by seasonal inundations and waterbody characteristics determine upon recruitment, the interactions of biota and shape the communities therein.
|Item Type: ||Thesis (PhD thesis)|
|Scharbert, Andreas Peteremail@example.com|
|Subjects: ||Life sciences|
|Uncontrolled Keywords: |
|Auen , Fische , Habitat , 0+ , Hydrologie||German|
|floodplain , fish , habitat , YOY , hydrology||English|
|Faculty: ||Mathematisch-Naturwissenschaftliche Fakultät|
|Divisions: ||Mathematisch-Naturwissenschaftliche Fakultät > Zoologisches Institut|
|Date Type: ||Completion|
|Date of oral exam: ||20 October 2009|
|Full Text Status: ||Public|
|Date Deposited: ||25 Oct 2010 14:07:36|
|Borcherding, Jost||PD Dr. habil.|
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